November 1, 2012 AT 5:00 am

EE Bookshelf: The Guerilla Guide to CNC Machining

The always knowledgeable Chris Gammell (of The Amp Hour fame) pointed me to one of the best CNC and mold making resources I’ve ever seen online, and while this may be old news to some people there’s an incredible collection of advice holed up in this article book: The Guerilla Guide to CNC Machining, Mold Making and Resin Casting by Michal Zalewski. If you’ve ever wondered how you can use a CNC mill to make custom gears, or just what the limits of a CNC mill are, this is probably the best online resource you’re likely to come across (note: feel free to prove me wrong in the comments below!).

I’ve been on the fence for years between buying a mid-range 3D printer or a mid-range CNC mill. They’re different solutions to (in my case) similar problems, but their respective advantages and disadvantages come close to cancelling each other out, which is why I still haven’t taken the plunge on either. My only interest is create prototypes of enclosures, or small mechanical parts like gears, and molds for silicon keypads or resin prototype parts, etc. A CNC mill is more flexible since a mid-range mill can also cut soft metals, and has a better finish than many affordable 3D printers, but you’re also more limited with the shape of the interior area compared to 3D printing.

If anyone out there has anything to contribute on the debate (in my head) between 3D printers and CNC mills, my guess is I’m not the only ‘maker’ in this same boat … where finish quality and price are important and it’s probably not realistic to just ‘buy both’. Feel free to chime in below with your own thoughts and experience!

Michael Zalewski is one of those people who are way too productive for their own good; puts the rest of us to shame. His robot building photosets on Flickr are a good browse (and his web security book is one of the gold standards these days).

Thanks for the book link Kevin. I will check it out. I too have been dithering between a CNC mill or router and a 3D printer.

Some of the latest generation extrusion machines shown at Maker Faire this fall were beginning to approach ‘acceptable’ finish quality – although still a far cry from what you can get from a mill.

Other advantages of a mill include a larger work envelope and the variety of materials (including wood & soft metals). The deal-breaker at this point is finding the shop-space for such a mill. I’d have to sell off some other machinery to make room.

One other comment: the reason I’m favoring the CNC milling approach over a 3D printer (which I’d love to have as well, but I only have so much dough): I can route a PCB with a CNC milling machine. There are plugins to take gerbers to gcode, so milling copper clad is a real possibility.

Definitely go for the mill first. It is more useful than a 3d printer. You can make high quality gears of any size on a mill and can cut your enclosures even if it isn’t CNC. If it is a CNC machine then you can do nice rounded corners and fancy features that would be hard or impossible if it were manual. You also aren’t limited to a small set of plastics.

I sell Taig (CNC) mills as one of my “day” jobs. CNC is far more versatile than 3D printing, at least on a hobby level. The problem is that there is a larger barrier to entry, as with 3D printing you just need to learn CAD and learn to use & adjust your 3D printer. With CNC you need to learn CAD, CAM, use and adjust the machine, as well as general machining techniques, jig&fixture work, precison measurement, etc. This is a good thing as once you start to master those skills there is very little that you can’t fabricate. I dont want to denigrate 3D printing as it is a useful technique, and becoming more versatile as time goes on, but I’m glad I went down the road of learning machining. Machined my first PCBs this week (I’m not just a dealer, I’m a user).

One of the things I’ve hoped to work on is a 3D printing toolhead that I can mount on my mill. The idea is to be able to build parts that are metal *and* plastic (using the 4th axis)….Or I can just put a build table on the machine, and have as much build area for traditional 3d printing as I want.

Another difference between the two platforms is tolerances. On a CNC mill you can get much tighter tolerances, so if you have tolerance requirements then I would say the CNC mill is the way to go. If you con’t care too much about tolerances and just want to prototype a part easier then 3d printing is the path to take. The thing with CNC mills (or regular mills for that matter) is the setup.

My father was a machinist and he would spend days setting up the jig necessary to make the parts he needed, both with numerical controlled and manual controlled mills. He told me that the hardest part of the job was reading the blueprints and picturing the necessary jig(s) to make the part.

"Don't worry about what anybody else is going to do… The best way to predict the future is to invent it. Really smart people with reasonable funding can do just about anything that doesn't violate too many of Newton's Laws!" - Alan Kay